Gas turbines are widely used in commercial operations for power generation. A typical gas turbine includes a compressor at the front, one or more combustors around the middle, and a turbine at the rear. The compressor and the turbine typically share a common rotor. The compressor progressively compresses a working fluid and discharges the working fluid to the combustors. The combustors inject fuel into the flow of compressed working fluid and ignite the mixture to produce combustion gases having a high temperature, pressure, and velocity. The combustion gases exit the combustors and flow to the turbine where they expand to produce work.
FIG. 1 provides a simplified cross-section of a combustor 10 known in the art. A casing 12 surrounds the combustor 10 to contain the compressed working fluid from a compressor (not shown). Nozzles 14 are arranged in an end cover 15 and an end cap 16, and a liner 18 downstream of the nozzles 14 defines a combustion chamber 20. A flow sleeve 22 surrounding the liner 18 defines an annular passage 24 between the flow sleeve 22 and the liner 18. The compressed working fluid flows through the annular passage 24 toward the end cover 15 where it reverses direction to flow through the nozzles 14 into the combustion chamber 20.
Ideally, the mass flow of the compressed working fluid inside the nozzles 14 is radially and circumferentially uniform. A uniform mass flow of compressed working fluid inside the nozzles 14 allows for a uniform distribution of fuel ports inside the nozzles 14 to evenly mix fuel with the compressed working fluid, thus providing a uniform fuel-air mixture for combustion.
Various nozzles have been designed to enhance the radial and/or circumferential distribution of compressed working fluid entering the nozzle. For example, FIG. 2 shows a cross-section of a prior art nozzle 26 with a bellmouth 28 opening. Fuel enters the nozzle 26 through a center body 30 that extends along an axial centerline 32 of the nozzle 26. A shroud 34 circumferentially surrounds a portion of the center body 30 to define an annular passage 36 between the center body 30 and the shroud 34. Swirler vanes 38 in the annular passage 36 may include fuel ports that mix fuel with the compressed working fluid flowing over the swirler vanes 38.
The bellmouth 28 shape increases the size of the opening leading to the annular passage 36, provides a smooth surface over which the compressed working fluid flows, and does not create a large pressure drop for the compressed working fluid entering the annular passage 36. However, computational fluid dynamic models of nozzles having a bellmouth 28 opening indicate that the mass flow rate of the compressed working fluid is concentrated around the center body 30 and diminished radially outward, particularly at the inside of the shroud 34.
FIG. 3 shows another prior art nozzle 40 having an inlet flow conditioner 42. The inlet flow conditioner 42 generally includes one or more baffles 44 and a perforated screen 46. Compressed working fluid flows through the perforated screen 46, and the baffles 44 redirect the airflow to improve the radial distribution of the compressed working fluid inside the nozzle 40. However, the inlet flow conditioner 42 shown in FIG. 3 is more expensive to manufacture and more difficult to assemble than existing nozzles. In addition, the inlet flow conditioner 42 increases the pressure drop of the working fluid as it passes through the nozzle 40.
Therefore the need exists for an improved nozzle design that can radially distribute the compressed working fluid entering the nozzle. Ideally, the improved nozzle design will enhance the radial and/or circumferential distribution of the airflow, not create a large pressure drop for the compressed working fluid, and will be relatively easy to manufacture and install in existing nozzle designs.